Generally, known printing machines comprise a rotatable carousel provided with a circumferential series of angularly-equidistanced chucks, each of which bears a single object to be printed upon.
The carousel rotates discontinuously at a constant angular step which is equal to the circumferential step separating the chucks.
In this way, each single chuck is located in a succession of work stations, to among which is one or more printing stations.
An inking means operates at each printing station, which can be a silk screen, a roller or another known means in the sector.
The inking means is located above the rotation plane of the chucks, and moves to release ink onto the lateral surface of the cylindrical object which, contemporaneously, rotates about itself, being activated by the chuck.
Once the inking stage has been completed, the cylindrical object is moved into a further work station, a drying station, where it is subjected to the action of a drying device, typically a lamp, for example an ultra-violet lamp, which dries the ink on the object, thus preventing running and imperfections in the design.
A requirement of this type of printing machine is that the inker should never be subjected to the action of the drying device.
Any such drying action would lead to drying up the ink on the inker itself, rendering further printing impossible.
For this reason, the drying device is generally located by a side of the inker means, and is oriented towards the cylindrical object located in the drying station.
A drawback of this arrangement is that the printing stations and drying stations must be separated by a rather wide gap in order to prevent the inker means being dried together with the object.
The gap, substantially unused, corresponds to a linear step separating the chucks of the rotatable carousel; the step in turn fixes the ratio between the number of chucks and the overall diameter of the carousel.
It follows that if the number of chucks is to be increased, and therefore the number of work stations, the overall size of the printing machine must also be proportionally increased.
As can be imagined, this is a very considerable drawback when, for reasons connected with the process, printing machines with many work stations and many chucks are to be realised.
The aim of the present invention is to obviate the above-mentioned drawback in the prior art, while at the same time guaranteeing that the silk screens are never subjected to the heat issued by the drying devices.
A further aim of the invention is to reach the above-mentioned objective by providing a simple, rational and economical solution.
The aims are attained by the invention in which a printing machine for cylindrical objects includes carousel means for moving for locating the cylindrical objects in a successive number of work stations, among which at least a printing station and at least a drying station, at least a means for inking for printing on the lateral surface of a cylindrical object located in the printing station, and at least a drying device for generating a beam of rays which strike a cylindrical object located in the drying station, wherein the drying device comprises an obturator for intercepting the beam of rays when the means for moving transfer the objects from one station to another.
Other particularly advantageous preferred embodiments, related to a silk screening machine, in which the drying device comprises a shield system for directing the rays only onto the cylindrical object located in the drying station. According to one embodiment, the drying station and the printing station are a single station. The drying device comprises a source of rays, and an upper screen provided with a slit, the slit screening the rays emitted by the source and delimiting the beam of rays. The slit is elongate and is arranged parallel to and vertically aligned with and below the cylindrical object located in the drying station. The slit is not longer than a longest cylindrical object processable by the machine. The slit is narrower than or equal in width to a diameter of a slimmest cylindrical object processable by the machine. The light source is a lamp according to one embodiment. The lamp is elongate and is arranged parallel to the slit. The machine further comprises an obturator for selectively closing the slit, the obturator comprising a cylindrical body arranged parallel with respect to the slit and having a diameter which is larger than a breadth of the slit, the cylindrical body exhibiting a diametral longitudinal slit which collimates with the slit. The cylindrical body is associated to actuator means which selectively place the longitudinal slit in an open position, in which the longitudinal slit collimates with the slit, and in a closed position, in which the longitudinal slit is angularly displaced with respect to the slit. The machine further comprises a detecting device of the position of the obturator. The detecting device comprises a mobile body, solidly fixed to the obturator, and a fixed proximity sensor for detecting a position of the mobile body. The upper screen is associated to means for cooling. The means for moving comprise a rotatable carousel provided with a circumferential series of chucks, each of which chucks can bear a cylindrical object.